When nuclear fuel is depleted, it must, of course, be removed from the reactor process area or core so that it may be replaced with fresh fuel. One current method for effecting removal involves introducing water under pressure into the tube holding the fuel charge. This causes the fuel charge to move through the tube to the end of the tube, where it is expelled. A fuel charge generally comprises about sixteen fuel elements arranged in the tube by spacers at either end.
When a charge/discharge operation is not in effect, the reactor tubes are typically sealed by an arrangement such as that shown in FIG. 1. In FIG. 1, the nozzle end of the process tube is indicated by numeral 10. The arrow in outline indicates a direction of flow. Nozzle cap 40 is threaded onto the nozzle 10. The nozzle 10 is also sealed by a seal plate 20 and graphoil seal 30. The seal plate 20 is loaded by three loading bolts 50, two of which are visible in FIG. 1.
When it is desired to effect fuel discharge, it is necessary for an operator to remove nozzle cap 40 and seal plate 20. This clears the way for the fuel charge to leave the process tube nozzle 10. A problem which exists, however, is that after the last spacer of the fuel charge has cleared the tube, water which has just traversed the radioactive core gushes out and sprays the operator. This imposes an undesirably high risk of radioactive contamination.
It is therefore desirable to provide a mechanism by which the nozzle 10 can automatically close after the final fuel spacer has cleared the tube. At the same time, it is necessary that any such mechanism function extremely reliably given the high safety standards required for nuclear reactor applications.